Transmitting high power signals using wireless transceivers may be challenging due to the inherent non-linear characteristics of power amplifiers provided within the transceivers. Indeed, power amplifiers typically have a limited linear region of operation for which their operating characteristics are predictable. For example, if the operating temperature and/or power level of a power amplifier falls outside a specified range, the power amplifier may begin operating in a non-linear manner that undesirably distorts data signals being amplified for transmission. The resulting signal distortion may cause data errors in the received data, and may overload (or even damage) front-end circuitry associated with the transceiver of the transmitting device. To compensate for the non-linear characteristics of the power amplifier, digital pre-distortion techniques may be applied to maintain signal power levels within certain ranges (e.g., by adjusting the gain of the power amplifier).
Many wireless devices include a loopback path that routes signals output from the power amplifier as feedback signals to a pre-distortion circuit, which in turn may process the feedback signals to determine a set of pre-distortion coefficients that represents the behavior of the power amplifier. The pre-distortion coefficients may be used to calibrate the power amplifier, for example, by pre-distorting data signals prior to amplification by the power amplifier.
Including a dedicated loopback path to route the feedback signals to the pre-distortion circuit may undesirably increase circuit area, especially for wireless devices that include multiple transceiver chains. In addition, the feedback signals may undesirably include parasitics of transmit and/or receive paths associated with the transceiver, which in turn may result in inaccurate pre-distortion coefficients.
Thus, it would be desirable to determine pre-distortion coefficients uncorrupted by transmit and/or receive path parasitics and without using dedicated loopback paths.